Group III-V compound semiconductor, such as gallium nitride (GaN), gallium arsenide (GaAs), indium nitride (InN), aluminum nitride (AlN) and gallium phosphide (GaP), are widely used in the manufacture of electronic devices, such as microwave frequency integrated circuits, light-emitting diodes, laser diodes, solar cells, high-power and high-frequency electronics, and opto-electronic devices. To improve throughput and reduce manufacturing cost it is desired to increase size (e.g., diameter) of substrates. Because growing III-V compound semiconductors of large size is very expensive a great number of foreign materials including metals, metal oxides, metal nitrides as well as semiconductors, such as silicon carbide (SiC), sapphire and silicon, are commonly used as substrates for epitaxial growth of III-V compound semiconductors.
However, epitaxy growth of group III-V compound semiconductors (e.g., GaN) on substrates (e.g., sapphire) poses many challenges on crystalline quality (e.g., grain boundaries, dislocations and other extended defects, and point defects) of the epitaxial layers due to lattice mismatch and coefficient of thermal expansion mismatch between the GaN layer and the underlying substrate, a foreign material. Differences in the coefficient of thermal expansion between the GaN layer and the underlying substrate result in large curvatures across the wafer, resulting during and post processing upon returning to room temperature, and the large mismatch in lattice constants leads to a high dislocation density, unwanted strain and defects propagating into the epitaxial GaN layer. In order to cope with these problems, stress relaxation strategies are employed, such as growing buffer layers between the GaN layer and the sapphire substrate, or counter balancing compressive and tensile strain by alternating appropriate material layers. However, by adding the buffer layer or stress relieving layers, the dislocation density may remain high and the manufacturing cost and complexity increases significantly because of the use of the same deposition techniques involved in growing the active device layers.
When foreign materials including metals, metal oxides, metal nitrides as well as semiconductors, such as silicon carbide (SiC), sapphire and silicon, are used as substrates for epitaxial growth of semiconductors, thin semiconductor films may be deposited on the substrate using molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) techniques, and in some cases using atomic layer deposition (ALD) or atomic layer epitaxy (ALE). By using these methods, however, not all atoms, ions, or molecules have an opportunity to organize themselves into regular arrangements, causing many atoms to form undesirable bonding orientations and significantly decreasing the crystalline quality along with negatively impacting electronic properties of the semiconductor materials. Crystalline quality is typically described in terms of crystal size, grain size, carrier lifetime, and diffusion lengths.
While some techniques such as Zone melt recrystallization (ZMR) are designed to improve quality crystalline material they may suffer from the drawback that the temperature generated for melting a portion of the deposited film may exceed the maximum temperature that can be handled by the underlying substrate. To prevent the underlying substrate from being heated to the melting point of the deposited film, the heating time may be shortened. However, shortening the heating time means that while solidifying, the crystal structure may grow in vertical direction rather than in both vertical and lateral directions simultaneously. Hence, epitaxial growth may be dominated in the vertical direction rather than the lateral direction resulting in patches of small grains along the substrate.